A patch antenna, for example, a microstrip patch antenna may provide a relatively a high gain for a given area using a relatively simple printed circuit construction, thus making its use widespread. One type of microstrip patch antenna has a radiation pattern that extends broadside to the patch plane. Such a microstrip antenna is commonly fed using a probe, for example, in the form of a connector pin or a circuit board via to form the probe that carries current to the patch surfaces.
However, the radiation bandwidth of a microstrip patch antenna may be limited. For example, the half power (3 dB) instantaneous gain bandwidth of microstrip patch antennas may be less than 20 percent in practice. This may be particularly disadvantageous compared to other types of antennas, such as parabolic reflector antennas, which can operate over many octaves of bandwidth. The frequency response of a simple, square, half wave edge, linearly polarized microstrip patch antenna may be described based upon the quadratic equation (ax2+bx+c=0) so there may be a “single hump” gain maxima located about a first, half wave resonance.
The bandwidth of a microstrip patch antenna increases linearly based upon the thickness of the substrate on which it is carried, so doubling the substrate thickness may double the bandwidth and halving the substrate thickness may halve the bandwidth. Unfortunately however, problems may arise in a broadband application using a relatively thick substrate microstrip antenna, as the feed probe can radiate in a manner akin to a monopole antenna. Given that the radiation pattern of a feed probe is different than that of the patch itself, the combined thick substrate patch radiation produces an asymmetric pattern and reduced realized gain.
U.S. Pat. No. 6,181,279 to Van Hoozen discloses a patch antenna with an electrically small ground plate using peripheral parasitic stubs. More particularly, Van Hoozen discloses the parasitic stubs or shielding element is for segregating electromagnetic fields between the patch antenna and the ground plate.
U.S. Pat. No. 5,515,057 to Lennen et al. is directed to a GPS receiver with an n-point symmetrical feed double-frequency patch antenna. More particularly, Lennen et al. discloses n symmetrical feed points that are placed geometrically on the patch antenna to achieve circular polarization of the GPS receiver with an n-point antenna.
Further improvements to patch antennas may be desired. For example, it may be particularly desirable to increase bandwidth, gain, directivity, and radiation pattern symmetry.